A raceway is the space immediately behind a tuyere of an ironmaking blast furnace, where a rotating flow of coke particles and gas is formed by the hot blast emerging from the tuyere. The temperature in the raceway zone is typically about 2000.degree. C. A number of raceways are evenly distributed around the furnace circumference, and their function is to generate and distribute hot reducing gases to the furnace burden. Stable furnace operation requires confinement of this hot, reducing gas flow to the furnace centre to prevent refractory damage and maintain stable burden descent.
Raceway depth and shape are fundamental determinants of gas and heat flow distributions in the packed bed of a blast furnace, thus exerting considerable influence on furnace operation and efficiency. Widespread availability of raceway depth sensing could be expected to have a significant impact by enhancing fundamental understanding of the processes occurring in the furnace combustion zone. From an operational standpoint, raceway depth measurement could be expected to contribute in the following areas:
control of peripheral uniformity of gas and heat flow PA1 in-situ assessment of the effects of variations in coke quality in the furnace high temperature zone PA1 control of hot metal silicon through optimization of the position of the cohesive zone PA1 optimization of casting practice via internal sensing of internal liquid levels. PA1 (a) It is invasive and may interfere with the dynamics of the raceway, thus causing a change in the very parameter it is meant to measure. PA1 (b) Flexing of the probe in the raceway introduces uncertainties in the measurements. PA1 (c) Repeated measurements on a routine basis are not practical After each measurement, the probe must either be retracted into the blow pipe or completely removed for cooling before another measurement can be made. PA1 (d) The technique cannot be used for making multiplexed depth measurements on a number of raceways For each raceway a completely separate measuring system must be used.
With reference to the second of these areas, it has been theoretically shown that raceway depth is a function of the coke mean size at the tuyere, and should therefore give a good indication of the coke quality in the high temperature zone. This relationship has been verified on both hot models an operating furnaces, but it is apparent that there is considerable disagreement as to the exact form of the correlation and significant scatter between the results obtained when measurements are made on a number of blast furnaces It seems likely that differences in raceway depth measurement methods contribute to this confusion , particularly considering the effect on the raceway of the invasive measurement methods employed to date.
Previous measurements of raceway depth have relied on the introduction of a water-cooled metal probe t tuyere. In these measurements, the raceway wall is assumed to have been reached when a predetermined wall pressure is observed or the probe stops moving While a single measurement can take less than a minute to make, repeated measurements are difficult and dangerous. Also the technique suffers from a number of other disadvantages:
More recently, theoretical predictions of the relationship between raceway depth and additional operational variables such as cohesive zone location and hearth drainage parameters have been made. Such modelling has the potential to greatly improve understanding but again it seems likely that raceway depth measurement technology which is adaptable to an operational mode must be developed if this benefit is to be secured. This then is the object of the present invention.